Hepatitis A virus (HAV) is endemic throughout the world, occurring most commonly, however, in areas of poor hygiene and low socioeconomic conditions. The virus is transmitted primarily by the fecal-oral route, and is spread by close person-to-person contact and by food- and water-borne epidemics. Outbreaks frequently occur in overcrowded situations and in high-density institutions and centers, such as prisons and health care or day care centers. Viral spread by parenteral routes (eg, exposure to blood) is possible but rare, because infected individuals are viremic for a short period of time (usually <3 weeks). There is little or no evidence of transplacental transmission from mother to fetus or transmission to newborn during delivery.

In most cases, antibodies to HAV (anti-HAV) are detectable by the time that symptoms occur, usually 15 to 45 days after exposure. Initial antibodies consist almost entirely of the IgM subclass. Anti-HAV IgM usually falls to an undetectable level by 6 months after HAV infection. Anti-HAV IgG levels rise quickly once the virus is cleared and may persist for many years. Currently, commercial diagnostic assays are available for detecting only anti-HAV IgM (HAVM / Hepatitis A IgM Antibody, Serum) or anti-HAV total (IgM and IgG), but not anti-HAV IgG alone.

A positive antihepatitis A virus (anti-HAV) total (both IgG and IgM) result indicates acute, recent, past/resolved exposure to hepatitis A, or immunity to hepatitis A from vaccination.

Testing for anti-HAV IgM (HAVM / Hepatitis A IgM Antibody, Serum) is necessary to confirm the presence of acute or recent hepatitis A. A positive anti-HAV total result with a negative anti-HAV IgM result indicates immunity to hepatitis A from either past/resolved hepatitis A or vaccination against hepatitis A.

Negative results indicate the absence of recent or past hepatitis A or a lack of immunity to HAV infection.

Borderline test results for anti-HAV total may be seen in: 1) acute hepatitis A with rising levels of anti-HAV IgM, 2) recent hepatitis with rising levels of anti-HAV IgG, or 3) cross-reactivity with nonspecific antibodies (ie, false-positive results). Retesting of both anti-HAV total and anti-HAV IgM (HAVM / Hepatitis A IgM Antibody, Serum) is recommended to determine the definitive HAV infection status.